Letter to the Editor
1. Paiva VC, Santana KR, Silva BM, Ramos PS, Lovisi JC, Araújo CG, et al. Comparação entre métodos de avaliação da modulação vagal cardíaca. Arq Bras Cardiol. 2011;97(6):493-501.
2. Zulfiqar U, Jurivich DA, Gao W, Singer DH. Relation of high heart rate variability to healthy longevity. Am J Cardiol. 2010;105(8):1181-5. 3. Thayer JF, Yamamoto SS, Brosschot JF. The relationship of autonomic
imbalance, heart rate variability and cardiovascular disease risk factors. Int
J Cardiol. 2010;141(2):122-31.
4. Mäkikallio TH, Tapanainen JM, Tulppo MP, Huikuri HV. Clinical applicability of heart rate variability analysis by methods based on nonlinear dynamics. Card Electrophysiol Rev. 2002;6(3):250-5.
5. Heitmann A, Huebner T, Schroeder R, Perz S, Voss A. Multivariate short-term heart rate variability: a pre-diagnostic tool for screening heart disease. Med Biol Eng Comput. 2011;49 (1):41-50.
References
Comparison of Assessment Methods of Cardiac Vagal Modulation
Marcos Antonio Almeida Santos
1,2, Antonio Carlos Sobral Sousa
1,2Núcleo de Pós-graduação em Medicina da Universidade Federal de Sergipe – UFS1, Aracaju, SE; Centro de Ensino e Pesquisa da Fundação São
Lucas2, Aracaju, SE - Brazil
Mailing Address: Marcos Antonio Almeida Santos •
Rua Dep. Clóvis Rollemberg, 598, Atalaia. Postal Code 49037-120, Aracaju, SE - Brazil E-mail: [email protected], [email protected]
Manuscript received March 2, 2012; manuscript revised March 2, 2012; accepted March 12, 2012.
Keywords:
Heart rate; assessment; autonomic nervous system. The theme “heart rate variability” (HRV) deserves to be continually studied by the scientific community, being one of our research lines. Regarding the article published in volume 97 (6), “Comparison of assessment methods of cardiac vagal modulation1”, the following is worth noting: A)
the samples were very different: older patients with coronary heart disease on beta-blockers versus healthy youngsters not treated with beta-blockade. Although the aim was to compare patients with coronary heart disease and healthy individuals, would the considerable age difference between
groups (approximately 40 years) not act as a confounding variable in the HRV values2?; B) the use of beta-blockers was
observed in 100% of the patients with coronary heart disease, as expected, considering the current guidelines, and in 0% of the healthy group. Autonomic modulation depends on a complex regulatory mechanism involving interaction between the sympathetic and parasympathetic pathways3,4. However,
after beta-blockade, the “modulatory” behavior of the vagus nerve is no longer spontaneous. Thus, would avoiding beta-blockers not provide more accurate results? C) time domain variables tend to be more precise in long-lasting registries5.
D) Of the variables selected to measure “vagal action”, would SDNN (standard deviation of normal RR intervals) not be better for studying the sympathetic nervous system? Finally, we congratulate the authors and thank the opportunity to shed some light into those questions.
Response letter
Dear Editor,
The interest in our recently published article1 brought us
great satisfaction. We appreciate the opportunity to respond to the editor’s considerations. It is worth emphasizing that our research group has been investigating that theme for over two decades2, with publications on the Arquivos Brasileiros
de Cardiologia, and that the scientific community has not reached a consensus yet (over 10 thousand publications on MedLine). First, it is worth noting that the selection of
groups with different clinical conditions and age brackets was intentional, aiming at selecting individuals with distinct cardiac vagal function. That selection was correct, because the differences in the characteristics of the groups reflect a greater cardiac vagal modulation (CVM) in the healthy group as compared with that in the group of patients with coronary heart disease with the three methods studied [Heart Rate Variability (HRV), Respiratory Sinus Arrhythmia (RSA) and Four-second Exercise Test (4sET)].
However, by analyzing the effect size and ROC curves, we observed that the RSA and 4sET methods, as compared with the HRV, were more precise to discriminate CVM among
Letter to the Editor
Arq Bras Cardiol 2012;98(6):569-570 Santos et al. Comparison of Vagal Assessment Methods
healthy individuals and patients with coronary heart disease. In that context, it is unlikely that the use of beta-blockers has influenced only the results obtained with the HRV. There is consistent evidence that beta-blockers increase CVM through both a direct effect on the central nervous system3 and a
peripheral effect, due to a reduction in heart rate, which increases the probability that acetylcholine acts on the slow diastolic depolarization of sinoatrial node cells4, and due to
a reduction in the pre-synaptic inhibition of the release of acetylcholine mediated by sympathetic activity5.
Thus, the beta-blocker-mediated increase in CVM is likely to have influenced the three methods assessed in the study and not only HRV, reducing the difference in the cardiac vagal function between the groups. It is worth noting that the assessment of patients on medications has increased not only the external validity of the results but the study applicability as well, since it is a similar situation to that found in clinical practice. Finally, the RR intervals were registered for ten minutes in a calm environment, with the individuals in the supine position and with controlled respiratory frequency.
In such conditions, the HRV results are more dependent on CVM, including the SDNN variable (standard deviation of normal RR intervals), and not on intervening variables6,
thus generating more reproducible results6. Differently, on
long-lasting registries, there is an influence of non-autonomic variables on the HRV results (ex.: temperature variations, hormonal variations), hindering the interpretation of the autonomic contribution.
Sincerely,
Vagner Clayton de Paiva Kelen Rabelo Santana
Bruno Moreira Silva Plínio Santos Ramos Júlio César Moraes Lovisi Claudio Gil Soares de Araújo Djalma Rabelo Ricardo
1. Paiva VC, Santana KR, Silva BM, Ramos PS, Lovisi JC, Araújo CG, et al. Comparação entre métodos de avaliação da modulação vagal cardíaca. Arq Bras Cardiol. 2011;97(6):493-501.
2. de Castro CL, da Nóbrega AC, de Araujo CG. Autonomic cardiovascular tests: a critical review. II. Arq Bras Cardiol. 1992; 59(2):151-8.
3. Vaile JC, Fletcher J, Al-Ani M, Ross HF, Littler WA, Coote JH, et al. Use of opposing reflex stimuli and heart rate variability to examine the effects of lipophilic and hydrophilic beta-blockers on human cardiac vagal control.
Clin Sci (Lond). 1999;97(5):585-93.
4. Martin PJ, Levy JR, Wexberg S, Levy MN. Phasic effects of repetitive vagal stimulation on atrial contraction. Circ Res. 1983;52(6):657-63.
5. Potter EK. Prolonged non-adrenergic inhibition of cardiac vagal action following sympathetic stimulation: neuromodulation by neuropeptide Y? Neurosci Lett. 1985;54(2-3):117-21.
6. Sandercock GR, Bromley PD, Brodie DA. The reliability of short-term measurements of heart rate variability. Int J Cardiol. 2005;103(3):238-47.
